The production of present day sausage products evolved historically from the manual stuffing of lengths of animal intestines with meat products to form selected lengths or links of the product for further processing such as smoking, curing, or cooking, or for use or retail sale. In modern sausage product manufacture, flexible tubular synthetic film casings are used extensively by the industry in making such products as frankfurters, link sausage, bologna, salami, various types of wursts, and in the packaging of ground and shredded meats, such as hamburger and poultry.
The casings with which this invention is mainly concerned are those made of synthetic materials which can be shirred to a self-supporting stick, that is to say casing materials with some degree of innate coherency. Such materials, without limiting the generality of the foregoing description, will include regenerated cellulose, cellulose derivatives, amylose, alginates, collagen, microporous plastic films, and films of polyethylene and polyvinylidene chloride, amongst others, the preferred materials being regenerated cellulose and the derivatives of cellulose. The tubing flat widths range from about 20 millimeters to about 33 millimeters, and tubing wall thickness are from about 1.06 mils to about 1.21 mils.
For convenience in handling, packaging, storing, transporting and utilization, relatively long lengths of tubing from about 10 to about 50 meters or more, are presently shirred and compressed into short lengths or sticks of about 15 to about 60 centimeters in length. Early on in the trade, these synthetic casings were hand shirred, albeit in somewhat shorter overall casing lengths, using hand shirring techniques such as had been traditionally used for shirring the natural or animal intestines casings.
This axial shortening or shirring of the casings is accomplished basically by the multiple folding or pleating of the tubing walls in a more or less accordion-like fashion by gathering an inflated tubing into pleats and then applying axial compressive force to pack the pleats into a tight interlocking coherent structure. Known methods of machine shirring comprehend passing the tubing over a hollow mandrel through which air is passed to inflate the tubing, and impinging lugs, cogs, chains, wheels or the like shirring elements on the tubing continuously in the direction of the longitudinal axis of the tubing to pleat it up and compress it against a yieldable restraining force.
The efficient manufacture of high quality casing sticks has developed into an art in itself, following, and sometimes in fact leading, the developments and advances in the ever forward movement of automatic sausage manufacture. Automatic stuffing and linking operations require precisely made sticks of consistently reliable structural integrity to insure against casing failure and consequent shutdown and loss of production. The sticks must be straight, coherent, flexurally stiff, and free from pinholes and structural deficiencies which could cause breakage during stuffing. It is additionally important that the sticks have sufficiently large and smooth internal bores to facilitate high speed stuffing on modern automatic stuffing equipment.
The criteria against which successful fabrication of shirred casing sticks is measured are:
(a) no damage to the tubing material,
(b) the finished stick is straight,
(c) the stick is coherent, i.e., it resists crushing or breaking under handling and packing stresses,
(d) the stick deshirrs evenly and smoothly with constant applied stuffing force,
(e) the stick is economically manufactured, and
(f) it can be consistently and reproducibly made to preselected standards.
Efforts to attain these goals and meet the criteria of successful shirred casing stick production have produced many technically advanced shirring techniques and apparatus as epitomized, for example, in the U.S. Pat. No. 3,779,284 to Tums, U.S. Pat. No. 3,695,901 to Winokur, U.S. Pat. No. 3,704,483 to Urbutis et al. and U.S. Pat. No. 3,461,484 to Arnold, all of which are illustrative of the general state of the prior art relative to the present invention. More recent developments are reflected in the shirring modes described in U.S. Pat. No. 3,988,804 to Regner et al, and U.S. Pat. No. 4,210,981 to Story.